1. Field of the Invention
The invention relates generally to communication networks. More particularly, the invention relates to methods and apparatus for utilizing AC powerlines as a communications media in such networks.
2. Description of the Prior Art
AC electrical wiring is already present in building structures to serve the building's power distribution needs. If this existing wiring could also serve as a communication media, it would provide a cost effective alternative for implementing local area communication networks. If such existing wiring could become high speed, reliable and cost effective as a communication media, the door would be opened for the development of many new applications. However, many hindrances have prevented the extensive use of powerline carrier technology in general purpose communication applications. Because of problems associated with communication speed, error rates, and implementation costs, AC powerlines have not had wide spread acceptance as a communications carrier. Others have attempted to solve these problems associated with powerline carriers. However, the prior art has not developed a cost effective implementation of high performance powerline carrier communication systems.
Demodulation of carrier data in wireless non-synchronized systems usually requires three forms of synchronization. First, proper reception of the message sometimes, especially when there are only a few carrier cycles per bit, requires carrier synchronization. A local carrier signal must be generated and synchronized to the received carrier signal. Secondly, proper demodulation always requires the receiver to determine the received data bit boundaries. This is referred to as bit synchronization. Thirdly, the receiver must determine the specific boundaries associated with each byte. This is referred to as byte synchronization. Proper packet reception requires achieving synchronization within or at the end of the preamble (the preamble consists of a specific data sequence preceding the packet body). The preamble serves as a signal to the receiver that a packet of information is being sent.
Powerline noise and other anomalies can cause incorrect synchronization. This in turn results in either incorrectly detecting the start of the data within the packet, or conversely not properly detecting the preamble. In either case the entire packet is lost. And often, incorrect detection of the start of the packet results in the loss of additional packets.